Engines operating with a variable number of active or deactivated cylinders may be used to increase fuel economy, while optionally maintaining the overall exhaust mixture's air-fuel ratio about stoichiometry via cylinder valve deactivation. Engines capable of deactivating a plurality of cylinders are commonly referred to as Variable Displacement Engines (VDE). Deactivating a cylinder may include disabling fuel injection and/or valve actuation in the cylinder. In some examples, half of an engine's cylinders may be deactivated during selected conditions. The selected conditions can be defined by parameters such as speed/load window, as well as various other operating conditions including vehicle speed. Increasing the time during which the vehicle operates with deactivated cylinders can increase the fuel economy of the vehicle.
However, in some engine/vehicle combinations utilizing variable displacement, only modest fuel economy gains are achieved. Various factors may limit the potential fuel economy gain, such as noise, vibration, and harshness (NVH) constraints. These factors may serve to reduce the available window of VDE operation, thus reducing potential gains. While various approaches of the skilled engine designer are aimed at reducing these limitations via enhanced design, fuel economy gains may nevertheless be difficult to realize in practice. In particular, the engine may be calibrated for worst case NVH conditions, thereby decreasing the available window for VDE operation.
In U.S. Pat. No. 7,104,244 an attempt is made to reduce NVH in a VDE during operation of a partial-cylinder mode. A time interval, identified as the “degree of continuation” parameter, is initiated when the torque produced by the engine exceeds a threshold value. If the degree of continuation increases above a threshold value, the partial-cylinder mode of operation is discontinued, due to a high probability that the vehicle is experiencing NVH.
The inventors herein have recognized several issues with the above approach. U.S. Pat. No. 7,104,244 utilizes a mode map to determine when the number of cylinders in operation should be adjusted. As noted above, such maps may be calibrated for worst case scenarios. For example, under certain conditions the vehicle may not experience NVH when it is being operated above a threshold torque, which may lead to unnecessary activation of a number of cylinders in the engine, further decreasing the fuel economy.
The above issues may be addressed by a method for operating an engine of a vehicle, the engine having one or more deactivatable cylinders, the method comprising: controlling the stability of a vehicle in response to vehicle acceleration; and reactivating or deactivating combustion in at least a cylinder in response to vehicle acceleration.
For example, the vehicle acceleration (e.g., lateral acceleration, yaw, etc.) can be used to not only improve stability of the vehicle; but also, for detecting engine vibration. Since the engine is coupled to the vehicle chassis, engine vibration can cause the vehicle chassis to exhibit acceleration. In particular, the engine firing-frequency component of the vehicle acceleration can be used to identify undesirable engine vibration. In turn, sensed engine vibration or acceleration can be used to appropriately control cylinder reactivation. In this way, it may be possible to better correlate NVH conditions and effects of partial cylinder operation. As a result, it is possible to improve vehicle fuel economy because the engine can be operated with fewer cylinders over extended operating conditions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.